Q: search field in Finder doesn't work

It's because you are looking for things in folders Spotlight cannot normally search. I would suggest you read this:

Helpful Links Regarding Malware Problems

If you are having an immediate problem with ads popping up see The Safe Mac » Adware Removal Guide and AdwareMedic.

Open Safari, select Preferences from the Safari menu. Click on Extensions icon in the toolbar. Disable all Extensions. If this stops your problem, then re-enable them one by one until the problem returns. Now remove that extension as it is causing the problem.

The following comes from user stevejobsfan0123. I have made minor changes to adapt to this presentation.

Fix Some Browser Pop-ups That Take Over Safari.

 

Common pop-ups include a message saying the government has seized your computer and you must pay to have it released (often called "Moneypak"), or a phony message saying that your computer has been infected, and you need to call a tech support number (sometimes claiming to be Apple) to get it resolved. First, understand that these pop-ups are not caused by a virus and your computer has not been affected. This "hijack" is limited to your web browser. Also understand that these messages are scams, so do not pay any money, call the listed number, or provide any personal information. This article will outline the solution to dismiss the pop-up.

 

Quit Safari

 

Usually, these pop-ups will not go away by either clicking "OK" or "Cancel." Furthermore, several menus in the menu bar may become disabled and show in gray, including the option to quit Safari. You will likely have to force quit Safari. To do this, press Command + option + esc, select Safari, and press Force Quit.

 

Relaunch Safari

 

If you relaunch Safari, the page will reopen. To prevent this from happening, hold down the 'Shift' key while opening Safari. This will prevent windows from the last time Safari was running from reopening.

 

This will not work in all cases. The shift key must be held at the right time, and in some cases, even if done correctly, the window reappears. In these circumstances, after force quitting Safari, turn off Wi-Fi or disconnect Ethernet, depending on how you connect to the Internet. Then relaunch Safari normally. It will try to reload the malicious webpage, but without a connection, it won't be able to. Navigate away from that page by entering a different URL, i.e. www.apple.com, and trying to load it. Now you can reconnect to the Internet, and the page you entered will appear rather than the malicious one.

An excellent link to read is Tom Reed's Mac Malware Guide.

Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.

See these Apple articles:

  Mac OS X Snow Leopard and malware detection

  OS X Lion- Protect your Mac from malware

  OS X Mountain Lion- Protect your Mac from malware

  OS X Mavericks- Protect your Mac from malware

  About file quarantine in OS X

If you require anti-virus protection Thomas Reed recommends using ClamXAV. (Thank you to Thomas Reed for this recommendation.)

From user Joe Bailey comes this equally useful advice:

The facts are:

1. There is no anti-malware software that can detect 100% of the malware out there.

2. There is no anti-malware that can detect everything targeting the Mac.

3. The very best way to prevent the most attacks is for you as the user to be aware that

     the most successful malware attacks rely on very sophisticated social engineering

     techniques preying on human avarice, ****, and fear.

4. Internet popups saying the FBI, NSA, Microsoft, your ISP has detected malware on

    your computer is intended to entice you to install their malware thinking it is a

    protection against malware.

5. Some of the anti-malware products on the market are worse than the malware

    from which they purport to protect you.

6. Be cautious where you go on the internet.

7. Only download anything from sites you know are safe.

8. Avoid links you receive in email, always be suspicious even if you get something

    you think is from a friend, but you were not expecting.

9. If there is any question in your mind, then assume it is malware.

Uninstalling Software: The Basics

Most OS X applications are completely self-contained "packages" that can be uninstalled by simply dragging the application to the Trash.  Applications may create preference files that are stored in the /Home/Library/Preferences/ folder.  Although they do nothing once you delete the associated application, they do take up some disk space.  If you want you can look for them in the above location and delete them, too.

Some applications may install an uninstaller program that can be used to remove the application.  In some cases the uninstaller may be part of the application's installer, and is invoked by clicking on a Customize button that will appear during the install process.

Some applications may install components in the /Home/Library/Applications Support/ folder.  You can also check there to see if the application has created a folder.  You can also delete the folder that's in the Applications Support folder.  Again, they don't do anything but take up disk space once the application is trashed.

Some applications may install a startupitem or a Log In item.  Startupitems are usually installed in the /Library/StartupItems/ folder and less often in the /Home/Library/StartupItems/ folder.  Log In Items are set in the Accounts preferences.  Open System Preferences, click on the Accounts icon, then click on the LogIn Items tab.  Locate the item in the list for the application you want to remove and click on the "-" button to delete it from the list.

Some software use startup daemons or agents that are a new feature of the OS.  Look for them in /Library/LaunchAgents/ and /Library/LaunchDaemons/ or in /Home/Library/LaunchAgents/.

If an application installs any other files the best way to track them down is to do a Finder search using the application name or the developer name as the search term.  Unfortunately Spotlight will not look in certain folders by default.  You can modify Spotlight's behavior or use a third-party search utility, EasyFind, instead.

Some applications install a receipt in the /Library/Receipts/ folder.  Usually with the same name as the program or the developer.  The item generally has a ".pkg" extension.  Be sure you also delete this item as some programs use it to determine if it's already installed.

There are many utilities that can uninstall applications.  Here is a selection:

    1. AppZapper

    2. AppDelete

    3. Automaton

    4. Hazel

    5. AppCleaner

    6. CleanApp

    7. iTrash

    8. Amnesia

    9. Uninstaller

  10. Spring Cleaning

For more information visit The XLab FAQs and read the FAQ on removing software.

Spotlight will not search in any system folders unless you configure it to do so:

Get Spotlight to search system files (and more)

1. Enter the search term in the Finder window's search field.
2. Click the [+] button in the search bar to add a search option.
3. In the first drop down menu choose Other.
4. Choose “System Files” from the list that pops up (and check the box to place in drop down menu to avoid this step later,) click on the OK button.
5. Now back in the Finder choose Include from the second drop down menu.

However, I prefer to use a third-party free utility, EasyFind 4.9.3, because it makes such searching easier. It does not require indexing files.

I think you need to read carefully and follow the instructions.